The construction of container ends drawn or formed from a metal sheet for use with metal containers are well-known in the prior art. Because of the high volume and the competitiveness in the industry for metal containers, there is a continuing search for improvements in the construction of containers and container ends which provide improved capabilities as well as improvements which provide a cost reduction, e.g., provide the desired construction or capabilities while employing a smaller amount of the metal.
Presently, container lids are produced by drawing or forming a flat, circular metal blank into a lid having a center panel, an annular groove, and an annular seaming panel. The annular groove is defined by an inner annular wall and an outer annular wall, with the top of the outer annular wall being joined to the annular seaming panel, the top of the inner annular wall being joined to the center panel by a panel radius portion, and the bottoms of the two annular walls being joined together by at least one bottom radius portion.
Jordan, U.S. Pat. No. 4,031,837, increases the strength of a conventional container lid by providing for a small radius of curvature in the bottom radius portion of the annular groove, which is uniform about the circumference of the annular groove. However, a disadvantage of an annular panel portion having a small radius of curvature is that the container lid is more prone to fracture, while a container lid having a larger radius of curvature is more prone to deformation caused by the pressure of the contents of the container. Therefore, a smaller radius of curvature strengthens the container lid against deformation but also subjects the lid to increased susceptibility to fracture.
Similar to strengthening the lid by providing for a smaller radius of curvature at the bottom of the annular groove, a container end can be strengthened by reducing the radius of curvature of the joinder of the center panel and the inner annular wall. This may make the inner annular wall more nearly vertical. However, the smaller radius of curvature of the joinder of the center panel and the inner annular panel also leads to an increased likelihood of metal fracturing at this joinder.
The metal blanks used to construct the container ends are produced in a blanking operation wherein metal blanks are cut from a sheet of metal. The nature of the rolling process used to fabricate the metal sheet used to produce the lids causes the physical properties of the metal sheet to vary at different locations depending on the angle from the rolling direction of the metal sheet. Because of the alignment of the grains of the metal in the sheet, the sheet is anisotropic, i.e., the tensile and shear strength of the sheet metal are not the same in all directions. However, the operation of forming a circular groove in a circular container end involves the application of forces along radial lines throughout the circumference of the groove. Hence, certain locations on the end blank are more likely to buckle (because of less structural rigidity) or fracture due to the orientation of that site on the end blank with respect to the rolling direction of the sheet from which the end blank is formed.
Thus, there is a need for a container end having a structure which takes into account differences in characteristics of the metal at different locations on the end blank with respect to the rolling direction. Additionally, there is a need for a die to produce the new container end.